CONTINUOUSWAVE

My [2002 Mercury 25-HP FOURSTROKE BIGFOOT engine had] sat for many years as a utility boat for a municipality. The engine ran "great" for about two outings but now the engine is getting "white oil."

The head gasket looks "good."

I changed the thermostat.

I cleaned the carburetor.

The [2002 Mercury 25-HP FOURSTROKE BIGFOOT engine] runs "great."

Now I am putting back together the [2002 Mercury 25-HP FOURSTROKE BIGFOOT engine].

I see a double gasket used on the head gasket.

If [seeing a double gasket used on the head gasket] does not solve [the engine "getting white oil"] then [the next remedy to try] looks like I'm heading for the base gasket.

The engine block [of the 2002 Mercury 25-HP FOURSTROKE BIGFOOT engine] was made by Yamaha.

A Yamaha base gasket works.

[In a future post I will announce] the part number and report back if the head gasket solved [the problem with the engine getting "white oil"].

Thanks for announcing that in the future you will post the part number of the Yamaha base gasket, and if that solved the problem of the engine "getting white oil."

I do not understand your sighting of "a double gasket". Is this sighting an observation of a mistake by some prior owner in servicing the engine?